The present disclosure relates to an image forming apparatus and a method of warning a life of a charging roller in the image forming apparatus.
Generally, an image forming apparatus of an electrographic type includes a charging roller facing to a rotatable image carrier and rotating to electrically charge the image carrier by rotating. The charging roller has a core metal part and an elastic part, such as electrical conductive rubber, formed at a side of an outer circumference face of the core metal part.
It is known that constant voltage is applied or constant current is fed to a circuit including the core metal part of the charging roller and electric resistance of the charging roller is calculated from measured value of current or voltage in the circuit.
Incidentally, if the charging roller is used for long time, it is feared that the core metal part is corroded. As temperature and humidity in using environment of the charging roller are higher, speed of advance of corrosion of the core metal part is accelerated. If the corrosion of the core metal part is advanced, dispersion of charging property in the elastic part occurs and exerts a bad influence on image quality.
That is, a lifetime of the charging roller is varied according to a condition of the using environment of the charging roller. The lifetime of the charging roller is a period during which the charging roller can be used without causing the bad influence on the image quality due to the corrosion of the core metal part. Therefore, it is important to estimate the lifetime of the charging roller and to output a warning urging maintenance, such as replacement of the charging roller, before using time reaches the lifetime.
Generally, as the corrosion of the core metal part is advanced, the electric resistance of the charging roller is increased. Therefore, it is known that constant voltage is applied or constant current is fed to the circuit including the core metal part of the charging roller and the electric resistance of the charging roller is calculated from measured value of current or voltage in the circuit to grasp corrosion condition of the core metal part on the basis of the electric resistance.
However, in a case where the corrosion is caused partly in the core metal part, because variation of the electric resistance of the charging roller is extremely small, it is difficult to detect extremely small variation of the resistance. Therefore, it is difficult to estimate in advance the lifetime of the charging roller from the variation of the electric resistance of the charging roller.